This invention relates to an optoelectronic memory, logic, and interconnection device with functions of memory, logic operation, and optical interconnection, which is based on an optical bistable circuit turned on and off with optical signals.
An example of optoelectronic memory devices operating with optical input and output is an image memory device described in the Japanese Patent Application No. 60-184047. This device is a two dimensional array of optical bistable switches, each of which is a series connection of a light emitting device and a phototransistor detecting the light emitted from the light emitting device. It functions as an image memory device which memorizes a two-dimensional pattern input with optical signals. It also outputs optical signals. This function is based on the characteristics of the optical bistable switch which emits light by itself when it is turned on with an optical input, and continues to maintain the on-state and emit output light after the input light is stopped. To reset the memorized contents, a power supply voltage is once set to zero. In case other optical signals are input without reset, the OR operation of two-dimensional patterns can be executed since the OR pattern of the first optical signals and the second optical signals are output.
Since the image memory device mentioned above is reset by setting the power supply voltage to zero, it is impossible to turn off the individual switches selectively. To improve this defect and make it possible to turn off the switch with an optical signal, an optical memory device was invented as described in Japanese Patent Application No. 60-151578. In this device, the second phototransistor is connected in parallel to the optical bistable switch and the optical bistable switch can be turned off by inputting light into the second phototransistor. The concrete structure of this device is shown in FIG. 8. A second phototransistor 5 is constructed with a first collector layer 2, a first base layer 3, an emitter layer 4 on a semiconductor substrate 1, and an optical bistable switch 10 is constructed of the emitter layer 4, a second base layer 6, a second collector layer 7, and active layer 8, and a cladding layer 9.
The input lights which turn on and off the optical bistable switch are incident through the semiconductor substrate 1. The energy bandgap of the first base layer is wider than that of the second base layer. The input light with a wavelength of .lambda. .sub.on satisfying .lambda..sub.1 &lt;.lambda..sub.ON .ltoreq..lambda..sub.2, where .lambda..sub.1 and .lambda..sub.2 are the wavelengths corresponding to the bandgap of the first and the second base layer, respectively, is transmitted through the first base layer and absorbed in the second base layer. Therefore, the optical bistable switch can be turned on with the input light having a wavelength of .lambda..sub.ON. On the other hand, the input light with a wavelength of .lambda..sub.OFF satisfying .lambda..sub.OFF .ltoreq..lambda..sub.1 is absorbed in the first base layer and can turn off the optical bistable switch.
In the optical memory device mentioned above, two input light sources are necessary to turn on and off the optical bistable switch since the wavelengths of the input light to turn on the switch and the input light to turn off the switch are different. Considering the case that the input lights for the first phototransistor and for the second phototransistor are distinguished not by wavelength but by spatial location, two light sources are still necessary.
Next, the background in relation to an optoelectronic interconnection device used for data transmission with optical signals is described. An example of such optoelectronic interconnection devices in shown in FIG. 9 which is demonstrated by S. Kawai et al. in the Conference Record of 1990 International Topical Meeting on Optical Computing, paper 10E7. In this construction, crossbar switching is attained by using an optical bistable switch array 12 in which optical bistable switches 11 with a function of light emission are arranged in a two-dimensional array, and a photodetector array 14 in which photodetectors 13 are arranged in a one-dimensional array.
The operation of the optical bistable switch is first described. The optical bistable switch has characteristics shown in FIG. 10 in relation to applied voltage and optical output power. When the applied voltage is below the holding voltage V.sub.H, it is always in the off-state and does not emit output light. On the other hand, it is always in the on-state and emits output light when the applied voltage is larger than the transition voltage V.sub.T. Considering the case that the applied voltage is between V.sub.H and V.sub.T, it is either in the "on" or "off" state. The output power in the on-state can be modulated with the applied voltage. Furthermore, the optical bistable switches 11 in the optical bistable switch array 12 can be addressed electrically since the anodes of these switches are wired along the column direction, while the cathodes are wired along the row direction. The bias voltage V.sub.A between V.sub.H and V.sub.T is usually applied between anode lines 17 and cathode lines 18. By increasing the potential of the selected anode line in (V.sub.T -V.sub.A)/2 and decreasing the potential of the selected cathode line in (V.sub.T -V.sub.A)/2, the optical bistable switch on the intersection of the selected anode and cathode lines is turned on selectively.
The operation principle of this device is described below. To perform data transmission using this device, the potential of the cathode lines are fixed and that of the anode lines are modulated between V.sub.A and V.sub.B (V.sub.A &lt;V.sub.B &lt;V.sub.T). Corresponding to this, modulated optical signals are emitted from the optical bistable switches in the on-state. These modulated optical signals are detected by the photodetectors 13 in the photodetector array 14. The optical signals from the optical bistable switches 11 along the same row are incident upon the same photodetector and converted to electrical signals. Therefore, the crossbar switching can be achieved because the electrical signals put into the anode lines along the column direction are converted to optical signals, which are again converted to electrical signals with the long photodetectors along the row direction, where the connection points between the column and row are determined by the position of the optical bistable switch in the on-state.
In practical operation, it is necessary to turn on the optical bistable switches on the connection points before starting the data transmission. To execute this, the potential of all the anode lines is first decreased in V.sub.A -V.sub.H to turn off all of the optical bistable switches. Then the potential of the cathode lines is decreased in (V.sub.T -V.sub.A)/2 one by one, when the potential of the selected anode line is increased in (V.sub.T -V.sub.A)/2. As a result, the optical bistable switches on the connection point are turned on selectively. After the selection of connection points with the reset signal and the address signal as mentioned above, the data transmission is started.
In the optoelectronic interconnection device mentioned above, the data transmission is interrupted to input the reset signal and the address signal always when the connection points are changed. The length of address signal and the period of interruption becomes longer as the number of switched lines becomes larger. Furthermore, in this device the data transmission with optical signals is only utilized for a very short distance between the optical bistable switches and the photodetectors, and all the inputs and outputs are electrical signals. In other words, this device minimally utilizes the merit of optical signal transmission, that is, free-space parallel transmission.